HOUSTON — The baseball schedule resumes in full on Friday, and the National League is a jumble, 10 teams within five games of a playoff spot. Yet the American League seems to offer just one hope for a pennant race: the plucky and powerful Oakland Athletics, the contender no one saw coming.

“That’s kind of how the A’s have always done it,” said veteran starter Brett Anderson, who pitched in the playoffs for Oakland, several teams and surgeries ago. “We’ve always kind of had that underdog role. It’s fun to be the spoiler and show people that we’re actually good and can compete with the best teams in baseball.”

The A’s finished last in the American League West in each of the last three seasons, a self-inflicted reset for a franchise that knows only extremes. On June 15, the A’s were 34-36, 11 games behind the Seattle Mariners for the second AL wild-card berth. They surged into the All-Star break with a 55-42 record, trailing the Mariners by just three games.

The New York Yankees, the Boston Red Sox and the Houston Astros are all cruising toward October, and the Cleveland Indians are the runaway leaders in a weak AL Central. But the Mariners have a negative run differential, and their regression may have already begun. The A’s, on the other hand, have outscored opponents by 24 runs.

“I texted Jerry Dipoto to congratulate him on his contract extension, and he wrote back, ‘Get off our tails!’” Oakland general manager David Forst said, referring to his counterpart with the Mariners. “But we’ve made it interesting, which is fun.”

Forst and Billy Beane, Oakland’s executive vice president of baseball operations, built playoff teams in 2012, 2013 and 2014. But the A’s never advanced in the postseason, and they quickly slammed their window shut, spending the next three years trading veterans for prospects and young major leaguers.

Now those players are making an impact, with homegrown talent like first baseman Matt Olson, third baseman Matt Chapman and utility man Chad Pinder, who has started at six positions this season. He takes five gloves on road trips.

“All the way up through the minor leagues, our core group was together,” Pinder said. “All the staff from each team, the managers and coordinators, they always instilled in us: ‘You win here, you win together, and it can and will translate.’ You’re seeing a little glimpse of that now.”

Last season, the A’s lost 12 of their first 15 games against Houston, the eventual World Series champion. But when they swept a four-game series against the Astros at home in September, manager Bob Melvin said, something felt different.

“They had just destroyed us completely at the beginning of the year, but then Pinder and Olson and Chapman and all those guys came up, and they weren’t part of that,” Melvin said in the visiting manager’s office after a win here last week. “These guys expect to win. So I learned enough about the team last year to have a good feeling about them.”

Besides Chapman, Olson and Pinder, though, Oakland’s 25-man roster at the All-Star break included just one other player who had entered pro ball with the A’s: pitcher Trevor Cahill, who drifted to five other teams between Oakland stints.

To contend so quickly after a tear-down process, and with a perpetually low payroll, the A’s have had to trade wisely. Mostly they have, especially for starters Sean Manaea and Frankie Montas and for All-Star closer Blake Treinen. In July 2015, the A’s traded starter Scott Kazmir to Houston for a package that included a catching prospect, Jacob Nottingham. They soon dealt Nottingham to Milwaukee for Khris Davis.

Davis, a designated hitter, has hit 106 home runs since the start of 2016, just three behind Giancarlo Stanton for the most in the majors. He has one season left before free agency and hopes to stay put.

Some players had Bay Area ties even before the A’s traded for them, like outfielder Stephen Piscotty and All-Star infielder Jed Lowrie, who both went to Stanford. Melvin has noticed a difference in the clubhouse, with fewer place holders and more players who genuinely want to be there.

The on-field formula is simple enough: power hitters and power relievers. The A’s lead the majors in home runs on the road, and setup man Lou Trivino has been a sturdy bridge to Treinen, who came to Oakland from Washington last summer — with top starting prospect Jesus Luzardo — for relievers Sean Doolittle and Ryan Madson.

The question now is whether the A’s can resist the temptation to promote Trivino to closer and sell high on Treinen. A wild-card berth, Forst suggested, was a powerful incentive for the front office.

In the big picture, though, it is business as usual for the A’s. While their executives have settled into modern offices in downtown Oakland, attendance a few miles away at the Coliseum ranks 28th in the majors. The A’s are opening the football seats in faraway center field for Saturday’s game with the San Francisco Giants, but a new venue is still far off. After years of fruitless haggling over building in San Jose, they have now targeted 2023 for a new home somewhere in Oakland.